1. Field of the Invention
This invention relates to a semiconductor light-emitting element and a method for producing the same.
2. Background Art
For improving brightness of a semiconductor light-emitting element, improvement of light taking-out efficiency is important. In a semiconductor light-emitting element, as one example of a structure in which high heat release property and high light taking-out efficiency can be expected, there is a flip-chip type structure in which a light-emitting layer side of a wafer is contacted with a heatsink side and the emitted light is taken out from the substrate side directly or with reflected by the reflection film.
The light emitted in the semiconductor light-emitting element changes its light pathway according to the incident angle to the interface having difference in refractive index. When the incident angle is such a deep incident angle as being near perpendicular to the interface, the light is taken out of the semiconductor element, and when a shallow incident angle, the light is totally internally reflected and returns to the inside of the semiconductor light-emitting element.
In the case of the flip-chip type semiconductor light-emitting element, for improving the light taking-out efficiency, it is thought that the light taking-out surface of the substrate is processed to be a dome shape and that nano-convex-concave structure having diffraction function is formed. However, for example, in the case of a semiconductor light-emitting element in which nitride semiconductor is formed on a sapphire substrate, refractive index difference between the substrate and the semiconductor layer is large, and therefore, in this structure, the light emitted in the semiconductor layer is reflected by its interface and easily trapped in the semiconductor layer. Therefore, even if the light taking-out surface of the substrate is devised, there is a room for upgrading improvement of the light taking-out efficiency.
For improving the light taking-out efficiency, it is also thought that the convex-concave structure is formed by processing the substrate surface on which the semiconductor layer is formed or by forming a non-flat layer in the semiconductor layer or by processing the surface of the semiconductor layer on which a reflective film will be formed. However, every method thereof requires advanced techniques, and additionally, these methods could leads to that the crystal growth condition for forming the convex-concave structure and the crystal growth condition for improving characteristic of the semiconductor light-emitting element are not highly compatible. That is, by forming the convex-concave structure, the crystal quality is degraded, and thereby, degradation of electric characteristic or optic characteristic is feared.
In JP-A 2007-5591 (Kokai), there has been proposed a structure in which the electrode combining with a function of a high efficient reflective film has a region having a width of ½ or less of a wavelength of the radiation light from the light-emitting layer.